We propose the continuation of experimentation directed at understanding the various control elements involved in the change of biosynthesis of cartilage proteoglycans during various aspects of development and aging of chondrocytes. Our primary focus will be on the characterization of proteoglycans produced by cells undergoing the transition between undifferentiated limb mesenchymal cells into newly committed chondrocytes. In addition, we propose to study the detailed biosynthesis of proteoglycans as chondrocytes progress through the expressional stages of their development history into senescence. Emphasis will be on the characterization and detailed chemistry of the core protein of cartilage proteoglycan with respect to how it interacts with the total biosynthetic pathway for proteoglycans. Such considerations must focus on the elements involved in the construction, maintenance and turnover of the extracellular matrix associated with chondrocytes. The studies proposed here deal with chondrocytes derived from chick embryonic and adult cartilages. Experimental characterization of the core protein of proteoglycans isolated from various sources involves a combination of immunological probes and detailed peptide fingerprinting. With the availability of this technology, we have outlined 6 individual projects. The experimentation represents a continuation of the technical procedures now current in this laboratory as well as the emphasis of new, recently acquired techniques involving use of antibodies and limited proteolysis to obtain analytical and qualitative information regarding the protein moieties associated with proteoglycan. The central theme of our research efforts is to provide insight into the molecular events involved in the commitment of mesenchymal cells into chondrocytes and the details involved in the expressional progression from an embryonic to a senescent cell.